Sligo, Leitrim and Donegal have some of the most overcrowded classrooms in the country.
New data shows that nationally, nearly one in 10 pupils are still in oversized classes of 30 or more, despite falling enrolments.
Average class sizes in primary schools have reached their lowest level in 20 years, with 4,000 fewer pupils in first-level education last year.
Some counties, including Leitrim, Donegal, Sligo and Monaghan, are more likely to have oversized classes, according to an analysis by the Irish Independent.
There were 27% of Leitrim pupils in classes of 30 or more in the recent school year, up from 18.6% in 2022-23.
Other counties with relatively high proportions of pupils in oversized classes were Donegal at 14.7% and Sligo at 14%.
